the thought of a bigger fence etc is fetching, but if you build a fort that no one can get into, HOW THE HELL DO YOU GET IT?.....you need to have open access to get out as well if SHTF..
You position these 'sally ports' in locations that give maximum chance to flank the enemy's likeliest direction of assault.
In a typical American home, this may be a side door leading from the garage to the front or back yard. These doors are often the portals into your home that home breakers/burglars/invaders use to gain access, so fortify them with deadbolt locks, a decorative metal security door fastened with lag bolts into the frame, or at a minimum a door brace.